# What is Circumference: Definition and 110 Discussions

In geometry, the circumference (from Latin circumferens, meaning "carrying around") is the perimeter of a circle or ellipse. That is, the circumference would be the arc length of the circle, as if it were opened up and straightened out to a line segment. More generally, the perimeter is the curve length around any closed figure.
Circumference may also refer to the circle itself, that is, the locus corresponding to the edge of a disk.

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1. ### How do I find the circumference and Area of this figure?

Hello! Consider this figure Where a = 5 cm. I need to find the Circumference and Area of this figure. For the Circumference I tried it like this. I have these 2 shapes, in red and in green For the green one its basically 2 times a quater of a circle so it should be  C_1= 2 * \frac{2\pi...
2. ### Concerning the 3d surface of a Hypersphere

Although 'undefined' it may be reasonable to assume that the hypersphere radius and circumference will respond to the normal relationship of a sphere i.e. 2 times Pi times r. Reasonable I suggest because the 3d surface of a hypersphere is a sphere. To get to my point, time and distance can be...
3. ### B Constructing a Line Segment Equal to a Circle's Circumference?

Is there any way to construct a line segment, that has the lenght of the circumference of a circle using only a ruler and a compass? My intuition says "no" Or phrasing the question in another way: given two line segments, can I prove, that the longer line segment has the length of the...
4. ### I Is the Ratio of Circumference to Radius of a Circle Always Irrational?

I take a string. It has a length, and that length is a real, rational number (let's call it an integer) I wrap it into a circle. Is it safe to say the radius is represented by an irrational number, too? Or is the "magic" (I would prefer not to use that word, but I go with it) of that number...
5. ### B Can I use the circle circumference formula for a sphere?

Trying to calculate a circumference of a sphere from a radius of 3.09 inches. Is 19.4 a correct answer? Just ran numbers in the first circumference calculator I found http://calcurator.org/circumference-calculator/. Can I use the same formula for a sphere? What can I say ...Geometry is not my...
6. ### Variance of a point chosen at random on the circumference of a circle

Hi, I was looking at this problem and just having a go at it. Question: Let us randomly generate points ##(x,y)## on the circumference of a circle (two dimensions). (a) What is ##\text{Var}(x)##? (b) What if you randomly generate points on the surface of a sphere instead? Attempt: In terms of...
7. ### I Possible simple formula for ellipse circumference

While fighting a CAD program, today, I might have stumbled on a potential way to easily calculate the circumference of an ellipse. I checked my method against a half a dozen online ellipse calculators and while my formula gives different results, I can't see where I'm making any logical errors...
8. ### Radius of circumference circumscribed to a triangle

At first I had no idea of how to solve this problem, but checking online I found out that there is a formula linking the radius of the circumference and the side of the triangle... the formula is: side=radius√3 The thing is that I can't understand why is this working... which deduction have been...
9. ### Finding the magnitude of the hydrostatic force per unit of circumference

Hello all I am trying to find the hydrostatic force of a cylindrical tank of water. I was hoping someone could help point me in the right direction. I have a cylindrical water tank. The dimensions are as follows:- I need to find the magnitude of the hydro static force per unit of...
10. ### A Relativistic Hoop w/ Constant Circumference: Solving Egan's Results

I wanted to re-do Egan's results for relativistic hoops with a different model, one with a relativistic hoop with a constant circumference. The idea is that by having the circumference not change as we spin up the hoop, we shouldn't be storing energy by "stretching" the material of the hoop...
11. ### Astrophysics: Calculating the circumference of an ellipse

Substituting : a = (9.15x10^7 mi)+(9.45x10^7mi) = 1.86x10^8 mi b = ( a/2 ) = 9.3x10^7 mi For this, I used six terms and got : 1.075x10^9 miles Is my math wrong?;
12. ### I Circumference of a circle on a spherical surface

I was just reading an intro text about GR, which considers the circumference of a circle on a sphere of radius R as an example of intrinsic curvature - the thought being that you know you're on a 2D curved surface because the circle's circumference will be less than ##2\pi r##. They draw a...
13. ### MHB Sun Circumference - A Picture on 04/18/2010

I took this picture on 04/18/2010, and I thought that I see the sun circumference. I just wonder can I calculate the physics and mathematics equations to figure out what is it that I am seeing in this picture. I stood from Earth standpoint, and I took this picture at noon time of the day.
14. ### MHB How to divide a circumference into equal parts, WITHOUT COMPASS?

Hi guys I have the length of a circumference, how do you divide it into equal parts given a certain amount of parts? For example, I want to divide a circumference into 78 equal parts, and the circumference diameter is 1 meter! Whats the length of each part? And how do you calculate it? (no...
15. ### Circumference of Circle with Uncertainty

Homework Statement Calculate the circumference (including uncertainty) of a circle whose measured radius is r=7.3 ± 0.2cm. 2.Relevant equations & 3.The attempt at a solution - Circumference of circle --> C = 2πr = 2π7.3 = 45.87 cm - Exact constant error propagation --> z =...
16. ### Find the derivative of a balloon's circumference

A balloon's volume is increasing at a rate of dV/dt. Express the rate of change of the circumference with respect to time (dc/dt) in terms of the volume and radius. Homework Equations Vsphere = (4/3)(π)(r^3) C = (2)(π)(r) The Attempt at a Solution [/B] My strategy was to come up with two...
17. ### I Derivative of the area is the circumference -- generalization

I thought you guys might appreciate this. A lot of people notice that the derivative of area of a circle is the circle's circumference. This can be generalized to all regular polygons in a nice way.
18. ### MHB Find radius, circumference, area and arc length in circle

So I've been able to solve A.12 inch B.24 inch C.75.3982 D.452.389 Cant solve e. Arc length can anyone please explain the formula. Thank you
19. ### Circle and a line dividing the circumference

Homework Statement The line "4x + 3y -4=0 " divides the circumference of circle centred at (5,3) in ratio 1:2.whats the equation of the circle Homework Equations 2πr Distance of a line from point Radius of general circle The Attempt at a Solution I tried finding the distance of the centre...
20. ### Understanding a book example about centripetal force

Homework Statement If the centripetal force is at the left side of the equation; that means if we move it over to the other side, it'll have a negative sign, which means it is opposite in sense in relation to N and mg. But how is that possible, considering that the centripetal force always...
21. ### Medical Giant neuron around circumference of brain?

http://www.sciencealert.com/a-giant-neuron-has-been-found-wrapped-around-the-entire-circumference-of-the-brain "For the first time, scientists have detected a giant neuron wrapped around the entire circumference of a mouse's brain, and it's so densely connected across both hemispheres, it could...
22. ### Calculating the Size of an Arbitrary Planet

Homework Statement You land on an unknown planet. The first night you note that its celestial pole is 40 degrees above the northern horizon at your current position. Your flight module is able to go 1000 km/hour. You fly an hour due south, and note that the celestial pole is now 30 degrees...
23. ### I Spectrum energy of a particle moving on a circumference

If you consider the one-dimensional case of a particle constrained to move on the edge of a circumference, the energy spectrum is continuous and two times degenerate. Why the fact that the particle can move in clockwise and counterclockwise implies that the spectrum is degenerate twice? In any...
24. ### Circle inscribed in a triangle exercise

Homework Statement In the drawing you can see a circumference inscribed in the triangle ABC (See the picture in the following link). Calculate the value of X https://goo.gl/photos/CAacV2dJbUrywfXv92. The attempt at a solution It seems I found a solution for this exercise with the help of a...
25. ### General Relativity and the Circumference of a Circle

Homework Statement Calculate the circumference of the circle θ = θ0 (a constant) in the spatial geometry \begin{eqnarray*} dS^2 = a^2(d\theta^2 + sin^2\theta cos^2\theta d\phi^2) \end{eqnarray*} Hence, (by finding R(z)) sketch the cross section of the surface embedded in three dimensions via...
26. ### Density and circumference relationship? From Example in book

Homework Statement Example 5.3 from The Marion Thornton book (fifth edition) of Classical Dynamics states the following problem: Consider a thin uniform circular ring of radius a and mass M. A mass m is placed in the plane of the ring. Find a position of equilibrium and determine whether it...
27. ### A Isotropic metric and circumference of sphere

Schwarzschild coordinates for the Schwarzschild black hole solution become very weird near the event horizon because the radial coordinate is based on the proper circumference of a sphere but that has a minimum at the event horizon. This is easy to see in isotropic coordinates, where the...
28. ### Finding the Radius of a Tangent Circumference in a Right Triangle

Homework Statement Let AC=5 and BC=12. In the triangle ABC, with angle C=90, point M is in AC. A circumference with center M and radius r is tangent to AB and tangent to BC in C. Set r. Homework Equations This should envolve basic trigonometry, and Thales' theorem; but not sure ( if I knew the...
29. ### B Understanding the Circumference of a Circle: A Comparison of 2π and 2πr

I just have a little question that i have read in the book of Thomas/Finney Calculus 9th edition that the circumference of a circle is 2pi,i can be wrong obviously but wasn't it supposed to be 2*pi*radius of the circle? Please help.
30. ### I Volume vs Circumference of Massive Body

Volume vs Circumference of a massive body. In the spacetime diagrams it is often shown that the space around massive bodies is warped in a way that seems to indicate the actual volume of a massive body is larger than 4/3 pi r^3. If you measure the radius from the circumference by traversing it...
31. ### B Ratio of circumference to diameter for infinitely large circ

If you divided the circumference of an infinitely large circle by its diameter, would the result be pi?
32. ### I Show that a particle moves over a circumference

The problem asks me to show that a particle moves over a circumference with its center at the origin. The position vector of a moving particle is: I've tried using the x2+y2=r2 formula of the circumference, squaring both components of the vector function but I couldn't figure out what to do...
33. ### Simple circle problem involving area and circumference

Homework Statement A stone is thrown into still water, forming ripples which travel from the center of disturbance in the form of circles. If the circumference of the circle which bounds the disturbed area is 10 ft and the circumference is increasing at the rate of 3 ft. per second, how fast is...
34. ### Calculate the distance travelled in a moving circumference?

First of all I don't mean a rotating circumference, but rather a translating one which is also rotating. Like this one: https://www.desmos.com/calculator/4vdymlzgpp just play the p button. I understand that the x component of the movement is: and Y= (where v is the radius, s is the angular...
35. ### About probability of crossing a circle circumference by a needle

Buffon`s needle problem described the probability of crossing a set of parallel lines with a known distance between them by a needle of a known length. What is the probability of crossing a circumference of a circle with a known radius by a needle of a known length? I feel that a simple answer...
36. ### Circle w/ circumference equals to that of an ellipse

Hi. Unfortunately, it looks like my first ever PhysicsForums post isn't even about Physics. I'll think of a Physics-related question later. :) Anyway, I know that each ellipse has an inscribed circle and a circumscribed circle, but I was wondering about a third circle associated with an...
37. ### Electric potential on circumference of charged ring

I heard that maximum electric potential for charged ring is at its circumference. Is there an expression to find the electric potential at any point on the circumference of a charged ring?
38. ### How to get the radius of a circumference given some points

Do you guys know of any program that can give me the radius of a circumference, if I input the cartesian coordinates of some points?
39. ### MHB Circumference and Area of A Circle

hello expert... How to find the circumference of a circle and area of a circle quickly? it's possible using method like ratio or series like pythagoras theory (3,4,5). or another way? somebody could help me out? cheers... susanto3311
40. ### Finding Circle Circumference from Inscribed N-Sided Polygen

The perimeter P of a regular polygon of n sides inscribed in a circle of radius r is given by P = 2nr sin (180^o / n). I was curious whether it's possible to approximate the circumference of a circle by taking the limit as n goes to infinity of the above perimeter equation is some way? Thank-you
41. ### Person walking on the circumference of a disc

Homework Statement A man is walking at a constant velocity v along the circumference of a disc which is pivoted at a point on it's circumference. The man starts diametrically opposite to the pivot and the disc starts at rest. The man and disc have the same mass. When the man reaches back to his...
42. M

### New way to find the Circumference of a Circle

While I haven't the right technology to find out if the measurement is absolute, it seems that by adding the measurements of A, B, C and D together, you get the circumference of a circle. (image attached)
43. ### Proving the Locus of Points Satisfying an Equation is a Circumference

The problem is: Let A, B and C be fixed points, and α,β,γ and κ are given constants, then the locus of a point P that satisfies the equation α(AP)2+β(BP)2+γ(CP)2=K, is a circunference. Prove it. I need at least some hint to answer it, I tried using the distance between two points formula but I...
44. ### Radius of circumference as function of arc lenght and height

Homework Statement I don't know the radius of the circumference. I could only measure the arc lenght, and the height. I know the guidelines say we should not post images, but this is a geometric problem and I think it is something logic to show it with a picture. So the variables are the...
45. ### MHB Find angles when circumference is divided into 5 unequal parts

Hello, I am using a very old textbook from 1895, Loney's Trigonometry, which poses the following problem: If the circumference of a circle be divided into 5 parts, which are in A.P., and if the greatest part be 6 times the least, find in radians the magnitudes of the angles that the parts...
46. ### Is outside diameter the same as circumference?

Okay, this might be a stupid question, but I have a sheet with all the formulas to find all kinds of anything you'd need to find about a gear. However I am confused by when it says outside diameter. Is outside diameter the same as circumference? How do I find outside diameter using either the...
47. ### Uniformly distributed around the circumference Loads (Statics and Mec)

Homework Statement My question is this, they say that at point B the 30kN force is uniformly distributed If a force is uniformly distributed shouldn't the units be 30kN/mIf so, wouldn't that imply the point force would act in the center of the disk and the force would be be 30kN multiplied...
48. ### Circumference of Earth With Eratosthenes

Homework Statement Eratosthenes measured the circumference of the Earth by noting that the Sun is at an angle of 7°12' = 7.2° ("one-fiftieth of a circle") south of the vertical in Alexandria at the same time of day and year that it is directly overhead in Syene. Syene is 5000 stades directly...
49. ### How did Eratosthenes measure the earth's circumference

Hello everybody, Eratosthenes of Cyrene ( 276 BC– 195 BC) was a Greek mathematician, geographer, poet, astronomer, and music theorist.The interesting thing about his biography,is that he was able to measure the Earth's circumference using only simple tools and good geometry .here is a video...
50. ### The circumference of an ellipse

I was wondering about how to find the circumference of an ellipse. I googled for it and found this: http://paulbourke.net/geometry/ellipsecirc/ That got me pretty amazed! I don't know high level maths, but still, can someone please explain to me why the circumference takes such a complicated...